Those involved in public entertainment such as theatrical production, musical performances, and the like have always depended upon stage lighting, back drops and similar props to produce the effect most conducive to the impression intended to be conveyed. Muscial groups, for instance rock bands, place heavy emphasis on special lighting effects, including flashing lights, to produce novel, psychedelic effects. Such performers often move from location to location, and therefore require light, portable equipment which can readily be transported and set up at the location of a performance.
Frequently, resort is had to lights suspended on horizontal bars or trusses mounted on telescoping tripod stands which can be extended to the desired height by means of an internal cable operated by a hand crank winch. Such systems are not only quite portable, but extremely versatile, inasmuch as the light supporting truss may be raised or lowered as required, and the numbers and types of lights hung therrefrom may be readily varied. The versatility of tripods of the type described has encouraged the use of multiple lighting arrays, some of which weigh as much as 200 to 300 pounds. As a consequence of such heavy loads, it is not uncommon for the tripod stand to experience failure of the operating cable, resulting in the sudden, unintended telescoping relapse of the supporting member carrying the lighting truss into the supporting sleeve of the tripod. The sudden checking of this percipitous downward movement when the supporting member reached the limit of its travel within the supporting sleeve usually dislodges the lighting fixtures, resulting in their destruction. Not only is the result a serious financial loss, but in those instances where the collapse takes place during a show, continuation of the performance is difficult and sometimes impossible.
In the past, an attempt has been made to avoid the problem by inserting pins through adjacent holes provided in the supporting sleeve and the supporting member, preventing relative movement therebetween. While the pins are effective in a static situation, they do not prevent the possibility of an accident when the safety pin has been removed during raising or lowering of the supporting member. At such times, however, particularly during raising of the supporting member, the probability of structural failure is at its highest due to the fact that the cable sometimes catches on an obstruction inside the members, resulting in over-design cable strains which are not detected by the operator due to the heavy weight of the lighting fixtures and the mechanical advantage of the winch. When the ultimate tensile strength of the cable is thus exceeded, it breaks, allowing the sudden drop of the supporting member within the supporting sleeve as previously described.